1. Field of the Invention
The present invention generally relates to a plasma display panel (PDP) which is a kind of light-emitting devices for displaying an image by using a gas discharge between glass substrates and, more particularly, to an improved structure of discharge sustain electrodes forming a pair of electrodes
a color PDP having an internal structure improved to increase aperture rate of the front panel which is an image displaying surface and maximize the efficiency of light emission using discharge between electrodes.
2. Discussion of Related Art
In general, color PDPs are a kind of light-emitting device for displaying an image by use of internal gas discharge and advantageous such as no needs to provide active elements in every cells, simple fabricating process, large-sized screen and high response speed. So, color PDPs are a promising display device having a wide screen, especially, wall TV and the next generation high definition television (HDTV) and used for television, monitor, interior/exterior advertisement display device and the like.
In addition, PDPs are easy to be enhanced in size relative to the existing liquid crystal displays and in the highlight in the field of large-sized display device to above 40 inches. The schematic structure of PDPs includes two glass substrates bonded together with a frit glass and sealed to form an integrated body.
Thus sealed internal space is filled with a gas under the pressure of 100-600 Torr and the gas is usually a fanning gas containing xenon (Xe) in helium (He).
The image display section of a panel has intersections between a plurality of electrodes in correspondence to the pixels (cells). When driving the panel, a voltage greater than 100 volts is applied to the intersections, causing glow discharge of gas and emitting lights, to display an image. This panel section is combined with a driving section to serve as a display device.
Such PDPs are classified into two-, three- and four-electrode types according to the number of electrodes allotted to each cell: the two-electrode type PDP is driven by applying an addressing and sustain voltage to two electrodes, and the three-electrode type PDP is generally called "surface discharge type" and switched or maintained by a voltage applied to the electrode positioned on the lateral side of a discharge cell.
An example of the related art three-electrode surface discharge PDP will be described below in reference with FIGS. 1 to 3.
FIG. 1 is an exploded view of a PDP structure having upper and lower substrates. In the figure, a front substrate 1 which is an image displaying surface is combined in parallel with a back substrate 2 at a predetermined distance.
The front substrate 1 is provided with a discharge sustain electrode formed with a pair of common electrode C and scan electrode S. The discharge sustain electrode is to sustain light-emission of cells by means of mutual discharge in one pixel. The front substrate 1 is also provided with a dielectric layer 5 for restraining discharge current of the two electrodes and insulating between electrode pairs, and a protective layer 6 formed on the dielectric layer 5.
The back substrate 2 includes a plurality of spaces for discharge, that is, separate walls 3 defining cells, a plurality of address electrodes A formed in the direction parallel with the separate walls 3 for performing address discharge at the intersections with scan electrodes S to cause vacuum ultra-violet rays, and a fluorescent layer 4 formed on the lateral sides of separate walls 3 and on the back substrates out of the internal surface of each discharge space for emitting visible rays to display images during address discharge,
The discharge sustain electrodes constituting a pair of electrodes are, as shown in FIG. 2, about 300 micrometers in width and include ITO electrode 7 and BUS electrode 8. ITO electrode 7 consists of a transparent material and causes a mutual surface discharge in the related discharge cell when a discharging voltage is applied to both terminals thereof. BUS electrode 8 being about 50 to 100 micrometers in width is made of metal and formed on the ITO electrode 7 in order to prevent a voltage drop caused by the resistance of the ITO electrode.
FIG. 2 illustrates the arrangement of common electrodes C, scan electrodes S and address electrodes A. And, FIG. 3 is a cross-sectional view of a cell after the upper and lower substrates are bonded together to form an integrated body, in which the lower substrate is rotated at 90 degrees expediently for better understanding.
First, when a discharging voltage is applied between scan electrode S and common electrode C that form a pair of electrodes in the cell, a surface discharge occurs between the two electrodes to form wall charges on the internal surface of the discharge space
Following the surface discharge, applying an address discharge voltage to scan electrode S and address electrode A causes a writing discharge to occur in the cell. Subsequently, a sustain discharge voltage is applied to scan electrode S and common electrode C, which causes a sustain discharge due to charged particles generated in the address discharge between address electrode A and scan electrode S, sustaining light-emission of the cell for a predetermined period of time
That means, the electric field is formed in the cell due to a discharge between the electrodes such that a minute quantity of electrons contained in the discharge gas are accelerated and collide with neutral particles in the gas to ionize, which are ionized into ions and electrons. Thus generated electrons collide with another neutral particles to produce more electrons and ions, The discharge gas is changed into plasma and vacuum ultra-violet rays occur. The generated ultra-violet rays excite the fluorescent layer 4 to emit visible rays, which are projected to the outside through the front substrate 1 to cause light-emission in a cell.
Especially, the related art discharge sustain electrodes have a structure in which BUS electrode 8 having a low resistance is formed in contact with high resistance ITO electrode 7. The most of voltage is applied via the low resistance BUS electrode 8 during a sustain discharge between scan electrode S and common electrode C so that the mutual discharge area (a) gradually appears from the center of the cell.
In such a conventional structure, however, the resistance of discharge sustain electrode affects the whole line uniformly and the discharge energy is consumed even at the boundary of the discharge cells that has little contribution to the discharge.
This reduces discharge efficiency in the discharge cells and adversely affects the luminance of images.